The problem. Serious HIV-associated neuropathology and the neurological side effects of Highly Active Antiretroviral Therapy (HAART) have been recently identified as the major hazards of chronic AIDS treatment. The important components of HAART, nucleoside reverse transcriptase inhibitors (NRTI), induce neurotoxicity due to the degradation of mitochondrial functions in peripheral and CNS neurons during long-term therapy. Since the treatment of HIV-1 located in phagocytic cells in CNS is far from satisfactory due to the blood-brain barrier (BBB) preventing drugs from reaching therapeutic levels in the brain, HIV-associated inflammatory processes make a negative impact on the viability of neurons and result in the development of HIV-induced encephalitis (HIVE) and dementia. The development of novel NRTI drug forms with reduced neurotoxicity and special approaches to their efficient delivery to the CNS is the major goal of this grant application. Hypothesis. Phosphorylated NTRI (pNRTI), as an active drug form, would be less toxic and more efficient drugs for the treatment of HIV-1 infection than the currently available NRTI. The major advantages of pNRTI, which will illustrate our choice, are as follows: (1) potential higher efficacy against HIV-1 in the infected host cells (macrophages, astrocytes, glial cells) deficient by kinase activities or against drug-resistant virus forms, (2) limited pNRTI access in mitochondria (lower mitochondrial toxicity), and (3) restricted cellular accumulation of negatively-charged pNRTI (reduced nonspecific toxicity). Since the majority of pNRTI are unstable in vivo, we hypothesize that the encapsulation of pNRTI in nanocarriers optimized for drug delivery across the BBB would provide efficient drug access to HIV-1-bearing peripheral or brain-harboring phagocytes. We have developed novel stable drug nanoformulations (Nano-NRTI), which can suppress virus multiplication more effectively than NRTI in macrophages and have a lower chance of accumulating in other tissues and exerting nonspecific toxicities. Modification with brain receptor-specific peptides or polyamines is proposed in order to enhance the cooperativity of Nano-NRTI binding with the BBB following drug administration. Nano-NRTI would then cross the BBB endothelium and release activated pNRTI in the brain parenchyma and brain-harboring macrophages. To address this hypothesis, we propose the following Specific aims: (1) to apply rational drug design and nanoengineering to the construction of nanocarriers loaded with pNRTI; (2) to optimize the antiviral effect and low cytotoxicity of Nano-NRTI in cultured macrophages, brain vascular endothelial cells, and neurons in vitro; (3) to enhance the efficiency of Nano-NRTI to cross the blood-brain barrier and accumulate in the brain; (4) to evaluate the effects of Nano-NRTI treatment on neuropathology in a mouse model of HIVE. Significance and impact. The less-neurotoxic version of HAART is likely to come from studies on rational drug design and targeted delivery. We develop a pNRTI-based HAART design (Nano-HAART), which enables the delivery of brain-targeted and oral activated drug formulations with reduced neurotoxicity into the CNS.